In recent years, Voice over Internet Protocol (VoIP) technology, also known as Internet Protocol (IP) telephony, has been adopted for conducting telephony communications over an Ethernet local area network (LAN). Compared to operating two separate communications networks, e.g. an Ethernet LAN for computer data communications and a PBX system for telephony communications in an office environment, a converged system by applying an Ethernet LAN for both data and voice communications would be highly desirable because it introduces network efficiencies for cost savings as well as for more tightly integration of data and voice applications.
Typically, most of today's Ethernet LANs are implemented as single-switch based systems in which a single Ethernet switch is used for switching both data and voice packets. The single Ethernet switch may comprises two or more physically separated Ethernet switches that are interconnected in certain way to operate as a single Ethernet switch. Usually, such an Ethernet switch may have to be provided with Quality of Service (QoS) and Virtual LAN (VLAN) capabilities as defined in IEEE Standard 802.1p/Q in order to support IP telephony communications.
However, such a single-switch based LAN presents several technical and operational issues and limitations which will make it difficult to deploy an IP telephony system over an Ethernet LAN. These technical and operational issues are briefly summarized as follows.    1) System reliability issue. Running data and voice communications over a single-switch based LAN is like “putting two eggs into one basket”. Once the LAN crashes or becomes paralyzed by malicious attacks of denial of services (DOS), both data and voice communications becomes unavailable at the same time.    2) Security issue. Although a VLAN can separate voice traffic from other non-voice traffic in a LAN for implementing a more secured IP telephony system, security is still a concern because the VLAN only logically separates voice traffic from other non-voice traffic at the data link layer of the Open System Interconnection reference model (OSI), a standard reference model for communications between end users in a network, and there are still chances that a VLAN setup maybe compromised and voice packets maybe intercepted and eavesdropped.    3) Networks upgrade issue. To upgrade an existing Ethernet LAN for IP telephony communications, the legacy Ethernet switches may have to be replaced with new Ethernet switches that are built with the QoS and VLAN capabilities. Routers and firewall deployed in the LAN may also have to be replaced as they may not be VoIP “friendly”, which would block in-bound callings. Such a forklift network upgrade is not only costly but also is likely to be very disruptive to the operation of the network.    4) Network management and maintenance issue. Migrating a legacy Ethernet LAN to a new LAN for IP telephony communications also introduces extra amount of workloads and costs associated with setting up and managing the new network. The network setup and management become much more complicated and time consuming because a lot more items and parameters related to the network behaviors and performances have to be configured and monitored, most of times manually by well trained and experienced IT professionals. The complexities and the need of highly trained IT personnel for setting up and managing an Ethernet LAN for IP telephony communications introduce hidden costs to the ownership of the overall network.    5) Remote diagnosis and trouble-shooting issue for supporting hosted VoIP (or IP PBX) services. A hosted VoIP service is a centralized telephony service offered by a service provider which has an IP PBX system installed at the service provider's location (e.g. a central office) and provides VoIP based telephony functions to a customer location via high-speed internet connections and the customer's internal network. A single-switch based internal network would make it extremely difficult for the service provider to look into the customer's internal network for remotely monitoring and trouble-shooting any system or service related issues because the service provider generally does not have any control over the customer's internal network.    6) Emergence 911 calls issue. In a traditional PBX system, a telephone is connected to a PBX port/line that is assigned with a fixed telephone number. This unique 1-to-1 mapping between a telephone number and a phone line or PBX port is used to track the physical location of the telephone. However, in an IP telephony system, the phone number of an IP phone is not associated with the port of an Ethernet LAN switch to which the IP phone is connected. Instead the phone number is assigned based on the Media Access Control (MAC) address of the IP phone itself. A MAC address is a physical address for identifying a device connected to a network. In other words, an IP phone can be connected to a different port of the LAN switch but still has the same telephone number. Such mobility nature of IP phones makes it difficult in tacking the location of the IP phone for supporting emergency 911 calling in an IP telephony system.
Meanwhile, because of the benefits of the convergence of data and voice communications over an Ethernet LAN, there are demands to resolve the above-mentioned technical and operational problems and limitations.